Polycarbonate (PC) exhibits high ductility (high impact strength), temperature stability over a broad temperature range, high stiffness, good dimensional stability, good electrical properties and a glass-like transparency. This material enjoys widespread use in various automotive applications, including headlamps, tail and sidemarker lights, and instrument panels. Polycarbonate is also used in bus windows and interior panels. Other uses include returnable milk bottles and electrical connectors. A potential use is in compact disks. The combination of high optical clarity and low breakability make polycarbonate a highly desirable material in certain applications such as automobile headlamps and tail lights and bus windows mentioned above. One drawback is that polycarbonate exhibits birefringence.
Polymethyl methacrylate (PMMA) also exhibits high optical clarity. In addition, polymethyl methacrylate also possesses good weatherability, good electrical insulating properties, good machineability and ease of assembly (e.g. by cementing or ultrasonic welding), and resistance to a variety of chemicals including acids, alkalies and household detergents. Dimensional stability is not outstanding, on the other hand. Uses of PMMA are many and varied. They include for example, automotive and bicycle lenses, table articles such as tumblers, aviation windows and canopies, skylights, retail displays, outdoor table tops, and window and door panels. The low level of birefringence of PMMA makes this material suitable for video disks and compact disks. However, the comparatively poor dimensional stability of PMMA suggests that new materials are needed for compact disk and video disk use.
Blends of polycarbonate (PC) and polymethyl methacrylate (PMMA) are known. However, references describing such blends invariably describe polycarbonate and polymethyl methacrylate as being immiscible in most proportions.
Z. G. Gardlund, in Polymer Preprints, vol. 23, pages 258-259 (1982) and American Chemical Society (ASC) Advances in Chemistry, Series 206, no. 9, pages 129-148 (1984) reports one or more indications of immiscibility in all PC/PMMA blends tested. Blend compositions ranged from 2 to 95 percent by weight PC, balance PMMA, on the dry basis. Visual observation showed that blends were opaque over the entire composition range, indicating polymer immiscibility, according to the Advances in Chemistry article. (The Polymer Preprints article describes a film prepared from a 2/98 PC/PMMA blend as being transparent).
K. K. Koo, et al, Polymer Eng. Sci., vol. 27, pp 741-746 (1985), describing mechanical properties of several two-phase polymer systems including PC/PMMA, shows that 90/10 PC/PMMA blends have higher impact strength and greater elongation at break than pure PC, and characterizes PC/PMMA as a "toughened alloy".
U.S. Pat. No. 4,319,003 to Gardlund observes that blends of PC and PMMA are opaque and do not possess the advantageous properties of either polymer, and proposes instead a block copolymer of PMMA and PC.